The studies of this project are those of the ongoing use of juvenile sheep for evaluating cardiac valve pathology and pathophysiology. Previous years' studies have concentrated upon conventional hydraulic/hemodynamic evaluations of native and prosthetic cardiac valves, and upon the morphologic and physical characterization of calcific degeneration of bioprosthetic valves. Efforts during the current year explored the following areas: (1) studies of homograft mitral valve substitutes; and (2) studies of Doppler determined intracardiac flow dynamics. The first studies have demonstrated the feasibility of homograft mitral valve replacement, providing a unique mode for investigating mechanisms of bioprosthetic valve leaflet degeneration and mineralization. The current studies have added credence to the hypothesis that preimplantation glutaraldehyde treatment facilitates mineralization. Two-dimensional, color-encoded Doppler evaluations of intracardiac flow dynamics using fundamental physical theories of jet flux and momentum continuity preservation have provided quantitative volumetric information regarding valvular regurgitation.